Dan, the 1976 match was in four sets. Nastase did not try in the last set.

Nastase had a bad habit of tanking whenever he felt that he was not being respected by the officials or the crowd, or if the crowd supported his opponent. He pulled the same stunt in the 1975 Canadian Open final against Orantes (Orantes was the crowd favourite in that match).
In Hong Kong, Nastase had lost the third set to Rosewall, and clearly gave up. I doubt that he could have won the match if he didn't tank, and he probably knew it himself.